1. Field of the Invention
The present invention relates to a transmitter, a transmission method, a receiver, a receiving method, a communication device, and a communication method which are applicable for a consolidated wiring of simple switching functioning parts such as switches or relays of a car (car) and sensors and so on.
2. Description of Related Art
As car electronics has been developed, an amount of wire harness used in a car has been increasing. This has brought problems such as an increase of car weight, an increase of difficulty in setting lines, and a deterioration in easiness of assembling operation. It also causes following problems. Space required for an ECU (Engine Control Unit) body is increasing because of an increase in a number of input-output lines for the ECU. Easiness of assembling operation is deteriorated because of an increase of power required for connecting the lines. Demands for performance of individual parts are increased because the ECU is mounted in a bad environment portion in order to deal with restrictions caused by the ECU body and an amount of the harness.
For example, there are a lot of switches connected to wirings arranged around a door of a high-quality car and a lot of ECUs are also arranged over separately because of a multi-functional trend of the car such as a door lock, a power window, a door mirror, and so on.
Therefore, the wire harness for the car so enlarged that it is difficult to further develop the car. A burden for a man-hour of soft development and management for arranging microcomputers separately is also greatly increasing.
As explained above, car equipments are getting multi-functional and complicated because they are required to be more comfortable and safer and more environmentally friendly. Accordingly, a number of control devices and electrical devices such as sensors and relays which are mounted on the car is increasing and a number of wirings for connecting these elements is also increasing. An increase in the number of the wirings causes an increase in the car weight and man-hour for setting. Therefore, various multiple communication methods have been suggested for decreasing a number of the wirings from past.
For example, a technique that superimposes a signal on a power line by performing spread spectrum in order to decrease a number of wirings and man-hour for setting is disclosed in Japanese Unexamined Utility Model Publication No. 62-122753 (hereinafter referred to as Takesaki et al.). A consolidated wiring device for car disclosed in Takesaki et al. includes means for performing spread spectrum processing on a transmission data by a PN (Pseudo Noise) code, means for superimposing a spread signal on the power line, means for performing inverse spread processing on the spread signal, and means for demodulating an inverse spread signal. More specifically, the consolidated wiring device for car checks status of each switch by a control circuit, edits a control data transferred to corresponding each terminal control device, and outputs the predetermined data. This data is converted to serial data by a SP (Serial-Parallel) converter. Further spread spectrum is performed on this data in a spread spectrum circuit. Tolerance against noise is strengthened by PN spread and malfunction is suppressed. The number of wirings and connectors is decreased by superimposing signals on the power line.
Technique for providing an intra-vehicle communication system having strong noise tolerance and simple wiring construction is disclosed in Japanese Unexamined Patent Application Publication No. 10-276170 (hereinafter referred to as Mori). The intra-vehicle communication system shown in Mori establishes communication between devices, which are mounted on vehicles such as busses, by performing spread spectrum processing. The intra-vehicle communication system includes one coaxial cable provided in the vehicle and a connector electrically connecting the consolidated cable with a plurality of devices that are provided corresponding to each of the plurality of devices. Only the dedicated consolidated cable is used for communication between devices thereby simplifying arrangement of wirings. Effect of noise is also reduced by performing the spread spectrum.
In techniques disclosed in Takesaki et al and Mori, a number of wirings is decreased by multiplexing communication between a plurality of control devices (ECUs) as shown in FIG. 11A. On the other hand, it is supposed that wiring for information transmission between cheaper switches or relays and control devices is still carried out one by one.
However wiring weight for this information transmission actually occupies large portion of a total wiring weight. In addition, a number of lines are remarkably increasing because the number of car equipments are increasing as mentioned above, so it is demanded to decrease a number of wirings. That is, it is required to multiplex communications between sensors or switches and the ECU as shown in FIG. 11B. When it is tried to apply techniques shown in Takesaki et al. and Mori to this case, problems are raised such as an insufficient of the number of PN spread code or of a communication speed.
The spread spectrum communication has a synchronous type and a non-synchronous type. There is a limit on a number of PN codes used in the non-synchronizing type. Therefore, the synchronizing type that uses an orthogonal code is preferable for connection having a large number of nodes.
Generally, communication speed of the spread spectrum communication is not a communication speed of data itself but a communication speed of an orthogonal matrix code gained by multiplying the communication speed of the data itself.
Length of the orthogonal matrix code becomes longer according to a number of connecting element. So, it is not avoidable to increase a whole communication speed in order to increase a number of connecting elements while holding a constant communication speed of data. On the other hand, there is an upper limit on a transmission speed of a signal in wire harness. Therefore, there is an upper limit on communication speed capable of holding synchronization in order to achieve a practical communication distance.
Therefore, communication speed for each node is a value gained by dividing upper limit value by a spread speed and the communication speed can be greatly slowed compared with a communication speed at one by one communication. Because there is a trade-off relationship between an increase in communication speed and an increase in a number of connections, it is difficult to achieve both of them.
By the way, a related communication device shown in FIG. 12 is known which superimposes a plurality of input signals and then transmits the superimposed signal. As shown in FIG. 12, the communication device performs PSK modulation at each PSK modulator 501a to 501c on input signals S111 to S113 at a plurality of channels respectively, performs PN spread at each PN spread unit 502a to 502c, and superimposes and transmits the signals. At receiving side, a SS invert spread unit 503 performs SS invert spread, demodulates at a PSK demodulator 504, and gains an output signal.
Signal waveforms in this case are shown in FIGS. 13A to 13F and 14A to 14E. FIG. 13A shows an example of input signals S111 to S113. FIG. 13B shows a signal S12 after PSK modulation is performed. FIG. 13E shows an enlarged view of FIG. 13B. FIG. 13C shows a signal S13 after PN spread processing is performed. FIG. 13F shows an enlarged view of FIG. 13C. FIG. 13D shows a signal waveform showing an example of PN code used in PN spread processing. PN codes that are specific to each channel are used.
FIG. 14A shows a signal waveform of superimposed signal S14 gained by superimposing spread signals from PN spread units 502a to 502c after PN spread processing is performed. FIG. 14D shows an enlarged view of FIG. 14A. FIG. 14B shows a signal S15 after SS invert spread. FIG. 14E is an enlarged view of FIG. 14B. FIG. 14C shows a signal waveform of an output signal S16 after PSK demodulation is performed.
Although it is possible to superimpose and transmit input signals in these methods, the maximum amplitude of signal shown in FIG. 14D is stacked according to a number of channels when signals after PSK modulation is performed are superimposed without no treatment. If an amplitude of 1 channel is −1 to 1 (v), an amplitude of a superimposed portion is set to −30 to 30 (V) and it is impractical.
Note that many techniques including a power line communication such as above-mentioned Takesaki et al. and Mori and so on adopt CSMA (Carrier Sense Multiple Access) system to avoid the amplitude of signals to be superimposed. The CSMA is one of communication system used for LAN (Local Area Network). In this CSMA, a node (device) monitors a communication status of a cable (Carrier Sense), and starts to transmit when the communication status of the cable is less busy.
If a plurality of nodes (devices) start to transmit data at the same time, the data may crash with each other and may be collision detection. In this case, the plurality of nodes stop transmitting data and start transmitting data after predetermined period of time. According to this method, it is possible to communicate mutually (Multiple Access) with sharing one cable with the plurality of nodes. However it is difficult to apply the CSMA type multiple communication which is not capable of successive communication to a communication that requires a successive data transmission such as above mentioned wire harness and so on in the car.